Nicolaus Copernicus was the first astronomer to formulate a scientifically-based heliocentric cosmology that displaced the Earth from the center of the universe. His epochal book, "De Revolutionibus Orbium Coelestium" - On the Revolutions of the Celestial Spheres - is often regarded as the starting point of modern astronomy and the defining epiphany that began the Scientific Revolution.

Although Greek, Indian and Muslim savants had published heliocentric hypotheses centuries before Copernicus, his publication of a scientific theory of heliocentrism, demonstrating that the motions of celestial objects can be explained without putting the Earth at rest in the center of the universe, stimulated further scientific investigations and became a landmark in the history of modern science that is known as the Copernican Revolution.

Among the great polymaths of the Renaissance, Copernicus was a mathematician, astronomer, physician, classical scholar, translator, Catholic cleric, jurist, governor, military leader, diplomat and economist. Among his many responsibilities, astronomy figured as little more than an avocation - yet it was in that field that he made his mark upon the world.

Copernicus proposed that the planets have the Sun as the fixed point to which their motions are to be referred; that the Earth is a planet which, besides orbiting the Sun annually, also turns once daily on its own axis; and that very slow, long-term changes in the direction of this axis account for the precession of the equinoxes.

This representation of the heavens is usually called the heliocentric, or "Sun-centred," system--derived from the Greek helios, meaning "Sun." Copernicus's theory had important consequences for later thinkers of the scientific revolution, including such major figures as Galileo, Kepler, Descartes, and Newton.

In the Commentariolus (Little Commentary), Nicolaus Copernicus outlined his revolutionary Copernican heliocentrism theory of the solar system, about three decades before he finally published his major six volume work De revolutionibus orbium coelestium in 1543. Copernicus did not publish the Commentariolus, and handed it only to few friends. It is unknown who received the Commentariolus, and when. He had written the preliminary manuscript description of his early version of the theory sometime before 1515. Some scholars believe it was as late as 1533 due to the maturity of the theory. It was never printed or otherwise published during Copernicus's lifetime, and its existence was only known indirectly until copies were published in the second half of the nineteenth century.

The only other astronomical work written by Copernicus, besides the Commentariolus and De Revolutionibus, was a letter written in 1524 to one of his former fellow students at the Cracow Academy, Bernard Wapowski (The Letter against Werner). This letter, which, like the Commentariolus, circulated in manuscript but was not published during Copernicus's own lifetime, criticized De motu octau¾ Sph¾r¾ tractatus primus, a work published in 1522 by Johannes Werner, which outlined a method of trepidations to account for purported variations in the rate of precession of the equinoxes.

The Commentariolus was known among scholars. In 1533, Johann Albrecht Widmannstetter delivered in Rome a series of lectures outlining Copernicus' theory. The lectures were heard with interest by Pope Clement VII and several Catholic cardinals. On 1 November 1536, Nikolaus Cardinal von Schnberg, Archbishop of Capua, wrote a letter to Copernicus from Rome, urging him to publish. Georg Joachim Rheticus and Tiedemann Giese[citation needed] then compiled an introduction to Copernicus' theory, the Narratio Prima, to be published by Franz Rhode in 1540. This was instrumental for Copernicus' approval to publish De revolutionibus.

The Name Copernicus

Numerous variants of Copernicus' name are documented. Until the mid-1530s, he mostly signed himself Coppernic. Afterward, he followed the academic custom of his time and adopted a Latinized version of his name. Thus, on the title page of his epochal book, Nicolai Copernici Torinensis De Revolutionibus Orbium Coelestium Libri VI, the astronomer's name appears as Nicolaus Copernicus.

In 1776, Johann Gottfried Herder introduced the spelling Nikolaus Kopernikus, which replaced each c with k and changed pp to p. This spelling became popular in German writings, although scholars argued for Coppernicus. The Polish rendering is Mikolaj Kopernik; the surname means "one who works with copper".

Early Life and Education

Certain facts about Copernicus's early life are well established, although a biography written by his ardent disciple Georg Joachim Rheticus (1514-74) is unfortunately lost. According to a later horoscope, Nicolaus Copernicus was born on February 19, 1473, in Torun, a city in north-central Poland on the Vistula River south of the major Baltic seaport of Gdansk. His father, Nicolaus, was a well-to-do merchant, and his mother, Barbara Watzenrode, also came from a leading merchant family. Nicolaus was the youngest of four children.

After his father's death, sometime between 1483 and 1485, his mother's brother Lucas Watzenrode (1447-1512) took his nephew under his protection. Watzenrode, soon to be bishop of the chapter of Varmia (Warmia), saw to young Nicolaus's education and his future career as a church canon.

Between 1491 and about 1494 Copernicus studied liberal arts--including astronomy and astrology--at the University of Cracow (Krakw). Like many students of his time, however, he left before completing his degree, resuming his studies in Italy at the University of Bologna, where his uncle had obtained a doctorate in canon law in 1473. The Bologna period (1496-1500) was short but significant. For a time Copernicus lived in the same house as the principal astronomer at the university, Domenico Maria de Novara (Latin: Domenicus Maria Novaria Ferrariensis; 1454-1504). Novara had the responsibility of issuing annual astrological prognostications for the city, forecasts that included all social groups but gave special attention to the fate of the Italian princes and their enemies.

Copernicus, as is known from Rheticus, was "assistant and witness" to some of Novara's observations, and his involvement with the production of the annual forecasts means that he was intimately familiar with the practice of astrology. Novara also probably introduced Copernicus to two important books that framed his future problematic as a student of the heavens: Epitoma in Almagestum Ptolemaei ("Epitome of Ptolemy's Almagest") by Johann Mller (also known as Regiomontanus, 1436-76) and Disputationes adversus astrologianm divinatricenm ("Disputations against Divinatory Astrology") by Giovanni Pico della Mirandola (1463-94).

The first provided a summary of the foundations of Ptolemy's astronomy, with Regiomontanus' corrections and critical expansions of certain important planetary models that might have been suggestive to Copernicus of directions leading to the heliocentric hypothesis.

Pico's Disputationes offered a devastating skeptical attack on the foundations of astrology that reverberated into the 17th century. Among Pico's criticisms was the charge that, because astronomers disagreed about the order of the planets, astrologers could not be certain about the strengths of the powers issuing from the planets.

Only 27 recorded observations are known for Copernicus's entire life (he undoubtedly made more than that), most of them concerning eclipses, alignments, and conjunctions of planets and stars.

The first such known observation occurred on March 9, 1497, at Bologna.

In De Revolutionibus,book 4, chapter 27, Copernicus reported that he had seen the Moon eclipse "the brightest star in the eye of the Bull," Alpha Tauri (Aldebaran).

By the time he published this observation in 1543, he had made it the basis of a theoretical claim: that it confirmed exactly the size of the apparent lunar diameter.

But in 1497 he was probably using it to assist in checking the new- and full-moon tables derived from the commonly used Alfonsine Tables and employed in Novara's forecast for the year 1498.

In 1500 Copernicus spoke before an interested audience in Rome on mathematical subjects, but the exact content of his lectures is unknown.

In 1501 he stayed briefly in Frauenburg but soon returned to Italy to continue his studies, this time at the University of Padua, where he pursued medical studies between 1501 and 1503. At this time medicine was closely allied with astrology, as the stars were thought to influence the body's dispositions.

Thus, Copernicus's astrological experience at Bologna was better training for medicine than one might imagine today. Copernicus later painted a self-portrait; it is likely that he acquired the necessary artistic skills while in Padua, since there was a flourishing community of painters there and in nearby Venice.

In May 1503 Copernicus finally received a doctorate--like his uncle, in canon law--but from an Italian university where he had not studied: the University of Ferrara. When he returned to Poland, Bishop Watzenrode arranged a sinecure for him: an in absentia teaching post, or scholastry, at Wroclaw.

Copernicus's actual duties at the bishopric palace, however, were largely administrative and medical. As a church canon, he collected rents from church-owned lands; secured military defenses; oversaw chapter finances; managed the bakery, brewery, and mills; and cared for the medical needs of the other canons and his uncle.

Copernicus's astronomical work took place in his spare time, apart from these other obligations. He used the knowledge of Greek that he had acquired during his Italian studies to prepare a Latin translation of the aphorisms of an obscure 7th-century Byzantine historian and poet, Theophylactus Simocattes.

The work was published in Cracow in 1509 and dedicated to his uncle. It was during the last years of Watzenrode's life that Copernicus evidently came up with the idea on which his subsequent fame was to rest.

Copernicus's reputation outside local Polish circles as an astronomer of considerable ability is evident from the fact that in 1514 he was invited to offer his opinion at the church's Fifth Lateran Council on the critical problem of the reform of the calendar.

The civil calendar then in use was still the one produced under the reign of Julius Caesar, and, over the centuries, it had fallen seriously out of alignment with the actual positions of the Sun. This rendered the dates of crucial feast days, such as Easter, highly problematic.

Whether Copernicus ever offered any views on how to reform the calendar is not known; in any event, he never attended any of the council's sessions. The leading calendar reformer was Paul of Middelburg, bishop of Fossombrone.

When Copernicus composed his dedication to De revolutionibus in 1542, he remarked that "mathematics is written for mathematicians." Here he distinguished between those, like Paul, whose mathematical abilities were good enough to understand his work and others who had no such ability and for whom his work was not intended.

Astronomical Work

The contested state of planetary theory in the late 15th century and Pico's attack on astrology's foundations together constitute the principal historical considerations in constructing the background to Copernicus's achievement.

In Copernicus's period, astrology and astronomy were considered subdivisions of a common subject called the "science of the stars," whose main aim was to provide a description of the arrangement of the heavens as well as the theoretical tools and tables of motions that would permit accurate construction of horoscopes and annual prognostications. At this time the terms astrologer, astronomer, and mathematician were virtually interchangeable; they generally denoted anyone who studied the heavens using mathematical techniques.

Pico claimed that astrology ought to be condemned because its practitioners were in disagreement about everything, from the divisions of the zodiac to the minutest observations to the order of the planets. A second long-standing disagreement, not mentioned by Pico, concerned the status of the planetary models. From antiquity, astronomical modeling was governed by the premise that the planets move with uniform angular motion on fixed radii at a constant distance from their centres of motion. Two types of models derived from this premise.

The first, represented by that of Aristotle, held that the planets are carried around the centre of the universe embedded in unchangeable, material, invisible spheres at fixed distances. Since all planets have the same centre of motion, the universe is made of nested, concentric spheres with no gaps between them. As a predictive model, this account was of limited value. Among other things, it had the distinct disadvantage that it could not account for variations in the apparent brightness of the planets since the distances from the centre were always the same.

A second tradition, deriving from Claudius Ptolemy, solved this problem by postulating three mechanisms: uniformly revolving, off-centre circles called eccentrics; epicycles, little circles whose centres moved uniformly on the circumference of circles of larger radius (deferents); and equants. The equant, however, broke with the main assumption of ancient astronomy because it separated the condition of uniform motion from that of constant distance from the centre. A planet viewed from the centre c of its orbit would appear to move sometimes faster, sometimes slower. As seen from the Earth, removed a distance e from c, the planet would also appear to move nonuniformly. Only from the equant, an imaginary point at distance 2e from the Earth, would the planet appear to move uniformly.

A planet-bearing sphere revolving around an equant point will wobble; situate one sphere within another, and the two will collide, disrupting the heavenly order. In the 13th century a group of Persian astronomers at Maragheh discovered that, by combining two uniformly revolving epicycles to generate an oscillating point that would account for variations in distance, they could devise a model that produced the equalized motion without referring to an equant point.

The Maragheh work was written in Arabic, which Copernicus did not read. However, he learned to do the Maragheh "trick," either independently or through a still-unknown intermediary link.

This insight was the starting point for his attempt to resolve the conflict raised by wobbling physical spheres. Copernicus might have continued this work by considering each planet independently, as did Ptolemy in The Almagest, without any attempt to bring all the models together into a coordinated arrangement. However, he was also disturbed by Pico's charge that astronomers could not agree on the actual order of the planets. The difficulty focused on the locations of Venus and Mercury.

There was general agreement that the Moon and Sun encircled the motionless Earth and that Mars, Jupiter, and Saturn were situated beyond the Sun in that order.

However, Ptolemy placed Venus closest to the Sun and Mercury to the Moon, while others claimed that Mercury and Venus were beyond the Sun.

In the Commentariolus, Copernicus postulated that, if the Sun is assumed to be at rest and if the Earth is assumed to be in motion, then the remaining planets fall into an orderly relationship whereby their sidereal periods increase from the Sun as follows: Mercury (88 days), Venus (225 days), Earth (1 year), Mars (1.9 years), Jupiter (12 years), and Saturn (30 years).

This theory did resolve the disagreement about the ordering of the planets but, in turn, raised new problems. To accept the theory's premises, one had to abandon much of Aristotelian natural philosophy and develop a new explanation for why heavy bodies fall to a moving Earth.

It was also necessary to explain how a transient body like the Earth, filled with meteorological phenomena, pestilence, and wars, could be part of a perfect and imperishable heaven. In addition, Copernicus was working with many observations that he had inherited from antiquity and whose trustworthiness he could not verify. In constructing a theory for the precession of the equinoxes, for example, he was trying to build a model based upon very small, long-term effects. And his theory for Mercury was left with serious incoherencies.

Any of these considerations alone could account for Copernicus's delay in publishing his work. (He remarked in the preface to De revolutionibus that he had chosen to withhold publication not for merely the nine years recommended by the Roman poet Horace but for 36 years, four times that period.)

And, when a description of the main elements of the heliocentric hypothesis was first published, in the Narratio prima (1540 and 1541, "First Narration"), it was not under Copernicus's own name but under that of the 25-year-old Georg Rheticus. Rheticus, a Lutheran from the University of Wittenberg, Germany, stayed with Copernicus at Frauenburg for about two and a half years, between 1539 and 1542.

The Narratio prima was, in effect, a joint production of Copernicus and Rheticus, something of a "trial balloon" for the main work. It provided a summary of the theoretical principles contained in the manuscript of De revolutionibus, emphasized their value for computing new planetary tables, and presented Copernicus as following admiringly in the footsteps of Ptolemy even as he broke fundamentally with his ancient predecessor. It also provided what was missing from the Commentariolus: a basis for accepting the claims of the new theory.

Both Rheticus and Copernicus knew that they could not definitively rule out all possible alternatives to the heliocentric theory. But they could underline what Copernicus's theory provided that others could not: a singular method for ordering the planets and for calculating the relative distances of the planets from the Sun. Rheticus compared this new universe to a well-tuned musical instrument and to the interlocking wheel-mechanisms of a clock. In the preface to De revolutionibus, Copernicus used an image from Horace's Ars poetica ("Art of Poetry"). The theories of his predecessors, he wrote, were like a human figure in which the arms, legs, and head were put together in the form of a disorderly monster.

His own representation of the universe, in contrast, was an orderly whole in which a displacement of any part would result in a disruption of the whole. In effect, a new criterion of scientific adequacy was advanced together with the new theory of the universe.

The presentation of Copernicus's theory in its final form is inseparable from the conflicted history of its publication. When Rheticus left Frauenburg to return to his teaching duties at Wittenberg, he took the manuscript with him in order to arrange for its publication at Nurnberg, the leading centre of printing in Germany.

He chose the top printer in the city, Johann Petreius, who had published a number of ancient and modern astrological works during the 1530s. It was not uncommon for authors to participate directly in the printing of their manuscripts, sometimes even living in the printer's home.

However, Rheticus was unable to remain and supervise. He turned the manuscript over to Andreas Osiander (1498-1552), a theologian experienced in shepherding mathematical books through production as well as a leading political figure in the city and an ardent follower of Luther (although he was eventually expelled from the Lutheran church).

In earlier communication with Copernicus, Osiander had urged him to present his ideas as purely hypothetical, and he now introduced certain changes without the permission of either Rheticus or Copernicus.

Osiander added an unsigned "letter to the reader" directly after the title page, which maintained that the hypotheses contained within made no pretense to truth and that, in any case, astronomy was incapable of finding the causes of heavenly phenomena. A casual reader would be confused about the relationship between this letter and the book's contents.

Both Petreius and Rheticus, having trusted Osiander, now found themselves double-crossed. Rheticus's rage was so great that he crossed out the letter with a great red X in the copies sent to him. However, the city council of Nrnberg refused to punish Petreius, and no public revelation of Osiander's role was made until Kepler revealed it in his Astronomia Nova (New Astronomy) in 1609. In addition, the title of the work was changed from the manuscript's "On the Revolutions of the Orbs of the World" to "Six Books Concerning the Revolutions of the Heavenly Orbs"--a change that appeared to mitigate the book's claim to describe the real universe.

Many of the details of these local publication struggles enjoyed an underground history among 16th-century astronomers long before Kepler published Osiander's identity. Ironically, Osiander's "letter" made it possible for the book to be read as a new method of calculation, rather than a work of natural philosophy, and in so doing may even have aided in its initially positive reception.

It was not until Kepler that Copernicus's cluster of predictive mechanisms would be fully transformed into a new philosophy about the fundamental structure of the universe.

Legend has it that a copy of De revolutionibus was placed in Copernicus's hands a few days after he lost consciousness from a stroke. He awoke long enough to realize that he was holding his great book and then expired, publishing as he perished. The legend has some credibility, although it also has the beatific air of a saint's life.

In cosmology, the Copernican principle, named after Nicolaus Copernicus, states 'the Earth is not in a central, specially favored position.' More recently, the principle is generalised to the relativistic concept that humans are not privileged observers of the universe. In this sense, it is equivalent to the mediocrity principle, with significant implications in the philosophy of science. Since the 1990s, the term has been used (interchangeably with "the Copernicus method") for J. Richard Gott's Bayesian inference-based prediction of duration of ongoing events, a generalized version of the Doomsday argument.

In the News ...

Scientists Say Astronomer Copernicus' Remains Found BBC - November 20, 2008
Researchers in Poland say they have solved a centuries-old mystery and identified the remains of astronomer Nicolaus Copernicus. A comparison of DNA from a skeleton in Poland and strands of the astronomer's hair found in a book in Sweden almost certainly confirm it is his skeleton. Archaeologists found the skeleton in north-eastern Poland three years ago in a cathedral where Copernicus lived. He worked in Frombork Cathedral on the Baltic Sea coast in the 16th Century.

Copernicus was one of the key proponents of the idea that the Earth orbits the Sun. For many years he was a canon and only carried out his astronomical studies in his spare time. People had speculated about his final resting place for centuries.

Three years ago, archaeologists dug up a skull and partial remains of a man aged about 70, Copernicus' age when he died, near an altar at the cathedral. Jerzy Gassowski, the leader of the archaeologists' team, said forensic facial reconstruction of the skull found that it bore a striking resemblance to existing portraits of the father of modern astronomy. Scientists then matched the DNA from one of the skull's teeth and a femur bone with two strands of Copernicus' hair. The hair was found in a book once owned by the astronomer now kept in Sweden's Uppsala University.